The toner used in electrophotographic printing machines is a blend of materials or ingredients, including plastic resins, coloring pigments, magnetic iron oxides, waxes, charge control agents, and other ingredients. Most toners are produced in bulk using a melt mixing or hot compounding process. The materials are typically fed by continuous loss-in-weight auger-type feeders into an extruder where they are blended together while in a molten state to thereby form a hot paste having a consistency similar to cake mix. This mixture is then cooled, typically by forming it into slabs on a cooling belt or by pelletizing the mixture in water. The pellets are then ground or pulverized into a toner powder by jet mills or air-swept hammer mills. This process produces a powder having a range of particle sizes. The toner powder is sieved or sifted to remove over-size and under-size toner particles, and may be blended with additives to adjust flow and electrostatic charging properties. The finished bulk toner is then packaged into end-use containers, such as toner bottles or cartridges, which are suitable for sale to and/or use by end users.
As discussed above, auger-type continuous loss-in-weight feeders are used to deliver the ingredients to the extruder. The auger-type feeders are often clustered together, and the multiple ingredients are fed into the extruder through a single extruder inlet. In such cases, side feeders/screw conveyors are often required since the relatively short auger-type feeders must be arranged in small feeder clusters, typically of two to four devices. The auger-type feeders typically require vibrators or agitators to promote the movement of the ingredients to the feeding auger. It can be difficult to achieve a consistent flow rate of such fine powdered ingredients through an auger-type feeder. Such powders may become fluidized, and flushing (uncontrolled flowing) of the fluidized powder through the feeder can occur. Therefore, the auger-type feeders generally require complicated control programs that are designed to adapt to the varying densities and flow characteristics of the powders as they move through the feeders.
After the toner powder is produced, it must be packaged. Packaging the toner or other powdered material into end-use containers generally involves the movement of the bulk toner from a filling hopper through a filling tube. The filling tube empties into toner bottles that have been conveyed into a toner bottle filling station. The toner is a fine powder that can have widely-varying bulk density and flow characteristics that may range from a dense cohesive powder to a low-density highly-fluid material. Conventional toner feeders/fillers typically involve moving the toner from one vessel to another by the force of gravity through vertically-oriented conduits that include an auger or a screw-feed system. Such auger-assisted, force-of-gravity systems are typically used to move the toner from the filler hopper through the filler tube and into the toner bottles. Since the toner tends to de-aerate or settle as it resides in a vessel or hopper, it can be difficult to obtain consistent gravimetric feed rates with auger-type feeders or fillers, which operate on a volumetric principle. On the other hand, highly-fluid toners may flush through an auger-type device and an uncontrolled flow or feed rate can result.
In short, the toner production process generally, and the bottle filling process in particular, has required that toner be fed from one vessel to the next utilizing either horizontal augers or auger-assisted force-of-gravity systems. Thus, for example, the bottle-filling hopper must typically be disposed above the bottle-filling station so that the force of gravity assisted by the auger moves the toner through the hopper, into and downward through the filler tube, and into the toner bottle. The need to feed toner from one vessel to the next by horizontal augers or by the force of gravity assisted by augers places substantial constraints on the process flow used to produce toner.
Further, the use of augers in the production of toner can have certain undesirable consequences. The augers must be precisely aligned, i.e., centered, relative to the funnel-shaped hopper outlet and extend through the outlet and into the filling tube and/or into the toner bottle. Even slight misalignment of the auger relative to the hopper outlet, filling tube, and/or toner bottle may bend the auger, causing the auger to seize. Augers may also bend during operation, installation, and during preventative maintenance. A bent or misaligned auger may rub against the funnel-shaped outlet, against the filler tube or against the toner bottle, causing toner to agglomerate or fuse on the auger. The agglomerated or fused toner may be dislodged and flake off from the auger into, and thereby contaminating, the packaged toner product. Bent or misaligned augers also require that the hopper and filling tube be emptied and cleaned. Seals used to seal the shafts of the augers become worn and fibers or lubricant from the worn seals may drop into and contaminate the finished toner product. Further, toner powder may penetrate through a worn seal, harden around the shaft, and then flake off into and contaminate the finished toner product, or may cause mechanical failure of bearings or other mechanical devices not intended to be exposed to toner.
The rotational speed or number of revolutions of an auger is often used as an indirect measure of the weight of toner dispensed into a toner bottle. However, toner powder de-aerates as it settles. On start up of the auger, toner particles in the hopper will be more densely packed and, therefore, more particles are carried by the auger. As the process continues and reaches a steady state, the toner particles are less densely packed and therefore fewer particles are carried by each revolution of the auger. Thus, the rotational speed or number of revolutions of the auger must be adjusted accordingly.
Therefore, what is needed in the art is a method and apparatus for controlling the flow and/or movement of bulk toner.